Dry granular mix



Patented Dec. 12, 1950 DRY GRANULAR MIX Wallace L. Howe, West Boylston,Mass., assignor to Norton Company, Worcester, Mass., a corporatlon ofMassachusetts No Drawing. Application July 30, 1949, Serial No. 107,821.v In Great Britain August 30, 1948 22 Claims. (01. 51304) The inventionrelates to dry granular mixes for the manufacture of abrasive products,to methods of making such mixes and to methods of making abrasiveproducts, the mixes being made out of abrasive material such as siliconcarbide or fused alumina and finely divided ceramic material such as aclay or clays for the production. after molding and firing, of vitrifiedabrasive products such as grinding wheels and the like. This applicationis a continuation in part of my copending application Serial No.681,769, filed July 6, 1946, and now'abandoned.

One object of the invention is to produce a dry granular mix from whichgrinding wheels and the like can be manufactured with automatic moldingmachinery.

Another object of the invention is to provide a dry granular mix of suchfree flowing characteristics that equivalent volumes will have the sameweight thus adapting the mix to molding by automatic means to yieldarticles having the same volume structure. Another object is to providea dry granular mix for rapidly producing grinding wheels in the greenstate, that need only to be fired in a kiln, for example, a continuoustunnel kiln. Another object of the invention is to provide a drygranular mix'of the character indicated which will make a strong, greenarticle. Another object is to make a dry granular mix of good moldingquality which is also relatively indifferent to changes in atmosphericconditions, so that for example the mix can be used in automaticmachines or the like for the manufacture of grinding wheels as well intropical and humid climates as in dry, cold climates. Another object ofthe invention is to provide a mix which shall not stick in the hopper,to the molding cavity or to the upper lunger or to the ejector.

Another object of this invention is to provide a mix which can behandled and stored for indefinite periods withoutv deterioration of itsmolding characteristics.

Another object of this invention is to make possible the production ofvery soft and porous structures.

Another object is to provide a dry granular mix from which uniformlyaccurately dimensioned abrasive and refractory articles can be made.

A general object of the invention is the high speed, low cost productionof grinding wheels and the like. Another general object of the inventionis the production of uniform vitrified abrasive articles byautomaticmachinery.

Other objects will be in part obvious or in part pointed outhereinafter.

The invention accordingly consists in the combinations of elements,arrangements of parts andin the several steps and relation and order ofone or more of said steps to one or more of the others thereof, all aswill be illustratively described herein and the scope of the applicationof which will be indicated in the following claims.

As conducive to a clearer understanding of the present invention,automatic machines for the continuous manufacture of pills, smallcylindrical articles and even medium large cylindrical articles up tosix inches in diameter are available on the market and have been formany years. Such machines, however, will quickly clog or fail toduplicate results in the manufacture of articles out of granularmaterial if the granular material is not free flowing, either generallyor under particular circumstances as on a humid day. Therefore a mix tobe usuable in such machines should be free flowing. Furthermore if themix sticks to the mold cavity or to the plungers, the machine willproduce one or many defective articles. Consequently the mix should havesuch characteristics that a complete green body is ejected every timethe ejecting motion of the machine operates. On the other hand, theparticles of the mix, after the pressing operation, must cohere to oneanother under pressure sufficiently to make a strong enough article. Inthe case of grinding wheels this cohesion imparts the so-called "green"strength to the article so that it can be handled, will not fall topieces of its own weight, and will maintain its shape .until firing inthe kiln vitrifies it.

For the manufacture of certain products in automatic molding machines ahomogeneous material is used. For example, in the manufacture of manyarticles, such as pills, the individual particles in the powder areusually finely divided and of the same order of magnitude regardless ofthe complexity of the substance from a chemical standpoint. Grindingwheels, however, customarily consist of at least two differentmaterials, the hard abrasive particles and the vitrified bondingmaterial which is made out of clays and other rocks, minerals and frits.This invention is concerned with grinding wheels and other abrasive orrefractory bodies made out of hard refractory abrasive grain bonded witha vitrifiable material, that is to say, a. material which can bevitrified in a kiln whether such material is made from clay or otherrock, mineral or frit, or any combination thereof, whether the materialis classified as a ceramic or a vitrifiable silicate or a combination ofoxides or otherwise.

Consequently, the material with which this invention deals consists ofcomposite particles each one being a particle of refractory abrasivematerial such as fused alumina or silicon carbide coated, in the usualcase, with hundreds or thousands of particles of vitrifiable material asabove described. According to the present invention wax is incorporatedto maintain the minute particles of clay or frit in adherence to eachother forming an envelope substantially coating and surrounding theabrasive granule. In a dry granular abrasive mix there should be aminimum of loose bond, that is to say bond not attached to an abrasivegranule and in accordance with this invention that objective isachieved.

In accordance with the invention I provide a quantity of abrasive grain.This may be particles of silicon carbide or particles of fused aluminaor other abrasives may be used, for example, corundum which is a naturalform of relatively pure crystalline alumina, or emery, or diamonds, forexample crushed bort.

The particle size of the abrasive material is not critical. However itis unusual for a grinding wheel to have less than several hundreds ofindividual abrasive granules and most grinding wheels have manythousands of individual abrasive granules. Furthermore, the commercialdemand for grinding wheels of grit size larger than 8 is small. The gritsize is the number of divisions in a linear inch of screen which willjust pass the abrasive of that grit size.

At the other end of the scale it is notvcustomary to use fines muchsmaller than 600 grit size. In the usual case, especially for wheelsunder seven inches in diameter which can be made with availableautomatic machinery grit sizes from 220 at the small end to around 16will be used, the bulk of the product being in the range between 30 and120 grit size.

I provide an abrasive mixing machine of any variety known to the art.Many varieties of mixer are known in the abrasive industry. In generalthese machines involve a container and something to stir the contents ofthe container. I prefer the type known as a vertical spindle mixer whichconsists of a vertical spindle, which is rotated, on top of which isfixed a disc-like table which removably holds a large open top pan intowhich the abrasive is charged. This mixer further has one or morestationary plows which are lowered into the pan. The rotation of the panand the stationary plows therein cause the granular abrasive material tofiow in tortuous paths so that a thorough mixing is achieved.

I next provide a quantity of vitrifiable bond as above described. Theparticles of this bond are small and should be not larger than one thirdof the size of the abrasive grains dimensionally. This bond should bevery dry and is placed in a hopper with a vibrator so that it can besifted into the pan. When the clay, rock, mineral or irit, orcombination thereof is thus sifted into the mixing pan which containsthe abrasive and which is turning, a thorough mixture of abrasive andbond results. But no attachment of the bond to theabrasive grain willoccur unless a further ingredient is added.

According to this invention, before the bond powder is added to theabrasive, I first add the wax which in one particular embodiment thereofis a wax emulsion. This, for example, may consist of 50% of ceresin wax(a microcrystalline paraflin wax) having a melting point of from 165 F,to 170 F. thoroughly emulsified to a creamy consistency with water andemulsifying agent, percentage being by weight. This wax since it has amelting point of from 165 F. to 170 F. will not soften during a hot daywhen, for example, the temperature of the mixing room may rise to 110 F.Any wax having a melting point above 100 F. might be used, but I prefera wax having a melting point above 150 F. It is really a matter of howhot the storage bins and the mixing room. etc., may become, and if theseare all air conditioned a lower melting wax can be used, but if not itis safest to use a wax melting above 150 F. There are many waxes so Ishould not be limited to particular ones. Further examples of usablewaxes will be given hereinafter.

As will hereinafter appear from the list of waxes given the chemicalnature of waxes varies. In my invention the chemistry of the wax is notimportant but the physical properties are important. Consequently it isnot possible to give a definition of wax" from a chemical standpoint butit is possible to give such definition from a physical standpoint,because it is the physical qualities that count with the exception ofthe fact that the wax must readily burn without leaving any deleteriousash during the firing operation. Accordingly any substance is a waxwithin this invention which isl. Substantially completely combustibleunder Unctuous Highly plastic and deformable Lacking in tensile strengthCohesive but only slightly adhesive Possessing a high coefficient offriction Non-elastic Crystalline Solid at room temperatures 0. Fusibleunder 300 F.

Accordingly, after the abrasive is placed in v the mixing pan, the plowslowered into position and the switches closed so that the electric motorrotates the pan, I add a quantity of the abovedescribed wax emulsion. Iprefer a quantity of around 6% by weight of the wax emulsion based onthe weight of the abrasive in the pan. However this may be varied fromaround 3% to 15%. In general with the smaller particle size of abrasiveI use more of the wax emulsion. For mixtures of about 60 grit size witha small amount of bond, 6% of the wax emulsion is the best proportionnow known to me, whereas with line grit sizes such as220 and a largeamount of bond I prefer to use about 12% of the wax emulsion based uponthe weight of the abrasive.

Mixing should be continued for about two minutes. This gives goodresults with the vertical spindle mixer rotating at 45 R. P. M. It isnot detrimental to continue the mixing for a longer time up to twice orthree times the foregoing, so if another mixer is used I recommend alonger period, for example, 10 minutes since this will not bedetrimental and may be desirable.

mamas I now add the bond while the pan is still rotating and the mixingis therefore continued. As above stated, the bond is slowly sifted intothe mixing pan and I continue until all the bond is in the pan and forabout three minutes thereafter. The length of time of mixing isdependent upon the revolutions per minute of the pan and the weight ofthe abrasive charge. For example, I might use a charge of abrasive ofabout pounds in a twenty inch diameter pan and a speed of around 45 R.P. M. for which a mixing time of three minutes after the bond is all inthe pan is satisfactory. Provided the pan is large enough to hold theabrasive without overloading, the plows are adequate, and the speed inR. P. M. is the same, the mixing time is about the same whether thecharge of abrasive be large or small.

As the result of the foregoing mixing there is produced a granular mixthe characteristics of which is. that every abrasive granule is coatedwith wax emulsion and bond, the wax emulsion and bond are thoroughlymixed, and there is no surplus of either wax emulsion or bond which isnot coated onto an abrasive granule. This mix however is not very dry.According to the invention the granular mix is now dried, but beforedescribing the drying and the result thereof I shall give preferredexamples of the bond.

For the manufacture of grinding wheels and other abrasive bodies amixture of clays has been used. For example, 20 parts of ball clay and50 parts of Albany slip clay and parts of feldspar, all by weight, arethoroughly dried, crushed, ground and screened. I may use the above in apreferred form of the invention or I may use more recently developedbonds, as to which I will refer to the patents which describe them. U.S. Patent No. 1,829,761 to Saunders, Milligan and Beecher, grantedNovember 3, 1931, describes an excellent vitrifiable bond especially forthe manufacture of wheels with fused alumina abrasive. U. S. Patent No.2,158,034 to Milligan and Lombard, dated May 9, 1939, describes anexcellent bond for the manufacture of wheels using silicon carbideabrasive. U. S. Patent No. 2,309,- 463 to Lombard and Milligan, datedJanuary 26, 1943, describes an excellent bond mixture for themanufacture of wheels with diamond abrasive. Many other bond mixturesfor the manufacture of vitrified bonded abrasive products will be foundin the patent literature, and I am not limited therein since anyvitrifiable bond may be used. All of the bonds described or referred toherein are ceramic bonds.

With regard to the quantity of bond to be used this depends upon thegrit size of the abrasive and structure of the grinding wheel to beachieved. Full instructions for the manufacture of abrasives of closelycontrolled structure are set forth in the U. S. Patent to Howe andMartin, No. 1,983,082, dated December 4, 1934. Accordingly, while thequantity of bond is certainly an important matter this is a variablefunction of the volume percentage of abrasive and bond and is now wellknown to the art, so in practicing the present invention I use an amountof bond as desired to produce the desired structure. The relative volumepercentages of abrasive, bond and pores depends not only on the weightpercentage of abrasive and the weight percentage of bond but also on theamount of compacting of the dry granular mix, and this is controllableby the adjustment of the automatic molding machine which is used to makegreen bodies out of the dry granular mix of the invention. Such machinesare not per se part of the present invention and the setting of themachine can be determined from the considerations in the Howe and Martinpatent which is referred to above.

After mixing as above described the mix or a quantity thereof ispreferably first screenedv and is then dried at a temperature of aboutF. The temperature should be at or slightly above the melting point ofthe wax in order to improve the uniformity of the mixture of bond andabrasive. With regard to the time, so long as the temperature is kept atthe limit indicated or below additional time does no harm. This dryingeliminates practically all of the water from the wax emulsion at leastdown to .1% or .5% of water on the total wax plus water. The abrasivegrains are now coated with dry wax and dry vitrifiable bond thoroughlymixed and there is no surplus thereof.

The mix is now carefully screened. If .the grit size of the abrasive was60, this will be increased to about 32 grit size by the addition of thewax and bond. In such case a screen of 32 meshes to the linear inchshould be used. A finer screen may cause an unmixing, and a coarserscreen will allow a cluster of two or more granules to pass through.

After the mix has thus been dried and screened,

it is recharged into the clean pan of the same or a similar verticalspindle mixer. The pan is set in rotation, the plows are lowered, andthen a quantity of anti-sticking agent is added. This anti-stickingagent functions to make the mix free flowing and it also functions toprevent the mix from sticking to the mold cavity or the plungers of theautomatic molding machine.

The preferred anti-sticking agent according to the present invention iscocoa. For example, finely ground cocoa beans may be used. The cocoabean contains cocoa butter which is an oily or fatty material, the cocoabutter content of such beans being in the neighborhood of 50% by weight.Consequently the ground product, which may be referred to as a meal, isof an oily nature and tends to lump together and aggregate in warmweather. Therefore I prefer to extract part of the cocoa butter from thebeans or from the meal and preferably down to about 22% of cocoa butter,and then there is no longer any storage difllculty and the product maybe kept on hand without refrigeration. I have found that it is betternot to extract all or nearly all of the cocoa butter since for somereason not fully. understood the presence thereof in quantities of fromaround 10% to 35% of the total weight of the meal is advantageous inthis invention. The preferred quantity of cocoa butter in the meal is asabove stated about 22%.

I may also use meal from any other seed which contains a natural oil orfat and most seeds do contain oil or fat which includes the esters suchas the butters. In such cases if the oil or fat content is greater than35% I prefer to extract some thereof to provide a meal having an oil orfat content between the limits above specified, namely from 10% to 35%and preferably to about 20%. But it should be understood that goodresults can be obtained using any of these meals provided they have afat content of at least 10% even though the fat content may be higherthan the limits indicated provided it is not more than 50%. Allpercentages are by weight and based on the total weight of the mealincluding the oil or fat or butter.

Examples of other seeds whose meals can be used are flaxseed (linseed),castor beans, rape seeds, and cotton seeds. Similarly meal made from thefollowing can be used: wheat (which becomes ordinary flour), nuts of allkinds, such as peanuts, walnuts, chestnuts, horse chestnuts, cashewnuts, Brazil nuts, pecans, Indian corn, otherwise known as maize, otherkinds of corn, rye, oats, barley and coffee. In every case the mealshould contain at least 10% and not more than 50% of the oily ester withwhich nature provided it. All of these contain an oily or fatty materialand in every case this oily or fatty material is the glycerine(glycerol) ester of a fatty acid. Since in each case the chemicalcomposi-- tion of the particular oil or fat is known it seemsunnecessary to give further definition thereof.

There are many ways of removing part of the oil or fat from thematerial. A customary manner of doing this is to press the beans orseeds whereupon some of the oil or fat runs off. This pressing operationmay also be the first stage in comminuting the material. Any method ofcomminuting, whether strictly a grinding operation or not, may beemployed or the beans or seeds may be disintegrated by chemicalprocesses. Other methods of extracting the oil or butter may be adoptedsuch as by the use of solvents for the oil or fat. Benzene C6Hs'is agood solvent for cocoa butter, but there are many others. It does notseem necessary to discuss all possible solvents for the oils or fatsinvolved since the case of cocoa a very finely divided or comminutedproduct having the cocoa butter extracted down to 22% of cocoa butter isavailable on the market and is the material preferred by me.

The grinding or other method of comminution should reduce the product toa particle size of which the major portion has a size not greater than100 microns. Furthermore less than of the material should have aparticle size as great as 200 microns. It is preferred that at least 50%of the particles should be no greater than 100 microns and no finer than3 microns and that 90% of the product should have a particle size nolarger than 200 microns. The remaining 10% can have any particle sizeprovided there are not more than one-half of 1% of particles larger than250 microns. The commercially available comminuted cocoa which I usefalls within this preferred definition and I have noted that in suchcocoa meal about 30% of the particles (by number) are individual cellsof the size of the order of 5 microns.

The quantity of anti-sticking agent to use in accordance with thisinvention will vary under different. conditions but in general thepreferred quantity is between one-quarter of 1% and 2% by weight. Thisis found to be the desirable range for cocoa and in general I use about1%. This range is also applicable to the other meals but strictlyspeaking it is the volume percentage which is the criterion and to findthe weight percentage of a meal whose specific gravity is significantlydiiferent from that of cocoa, you would first find the volume percentagethereof corresponding to the preferred volume percentage of the cocoa.This of course can readily be calculated from the specific gravities ofthe materials respectively. I may also observe that with the coarsergrit sizes of abrasive the amount of anti-sticking agent is preferablytoward the lower limit and with the finer grit sizes of abrasive theamount of anti-sticking agent is preferably toward the upper limit.

When the envelopes of ceramic bond and wax are coated with any or theanti-sticking agents, the individual particles of abrasive bond and waxcoated with anti-sticking agent will not stick to the mold or to thedies of the molding machine. Yet when the plunger or die operates, thewax containing envelopes of the particles flow together to form acontinuous phase of bond and wax thus making an integral green article.

Continuing now with the steps in the process, the mixing is continuedafter all the anti-sticking agent is added for about one half minute andit is undesirable to continue much longer. A shorter time would givesome results but little is gained from being niggardly in this respect.The mixing is now completed and the mix may be dumped and used asdesired. I have not found that any further screening is necesary but iflumps do occur, further screening would be indicated.

Thus each particle of the dry granular mix consists of a central nucleusof hard refractory abrasive, such as silicon carbide or fused alumina,coated with a thorough mixture of dry vitrifiable bond powder and a dryadherent wax, this coating forming an envelope enclosing the abrasivewith a further very thin coating of the antisticking agent which adheresto the waxy particles of the adherent wax by reason of being practicallyembedded therein, but which offers no adhering attraction for otherunits by reason of the non-adhering, non-tacky qualities of theantisticking agent. Likewise the anti-sticking agent repels water.

This dry granular mix may now be handled with trowels or the like andcharged into the hopper of an automatic molding machine which can. thenbe set in operation and will turn out at a rapid rate pressed and formedgreen" wheels or other shapes ready for the kiln. Such green shapes haveenough strength to be easily handled and in fact are exceptionallystrong. They may be placed on refractory batts, each batt holding anumber of them and then the batts can be loaded into a continuous tunnelkiln for vitrizfying for example at cone 12, and there emerges from thecontinuous kiln vitrified grinding wheels which are ready for use assoon as they have cooled down. With accurately dimensioned moldingequipment so accurate is the manufacturing process when using my drygranular mix that truing and siding of the wheels may often be dispensedwith and I have found in practice that I can hold them in diameter,thickness and diam er of central hole and roundness to within three orfour thousandths of an inch.

During the pressing operation the coating of the anti-sticking agent isruptured and the bond coheres because the wax sticks together, joimnggranule to granule and forming a compact integral green article whichcan be readily handled. Prior to the pressing, however, the granuleswill not stick to each other nor to the parts of the machine, nor willthey attract moisture.

As previously stated waxes other than ceresin wax can be used. Undersome conditions any wax having a melting point above 100 F. can

, be used, but in most cases the wax should have Other methods oftreating the materialto incorporate the wax in the bond may be employed.I can use a water soluble wax which may be dissolved in water withreasonable stirring. The procedure when using a water soluble wax isfirst to charge the mixing pan with the abrasive and start the mixingmachine in operation; second, add the desired quantity of the waxdissolved in water and continue the mixing until all the grains arecoated with the solution; third, sift in the bond while continuing themixing; fourth, after the grains are coated with bond as well as wax,dump the mixture and dry it in an oven or on a belt conveyor; fifth,screen the mixture until each granule coated with bond and wax is adistinct particle; sixth, recharge the screened mix into a clean mixingmachine and set the machine in operation; seventh, sift in theanti-sticking agent while continuing the mixing.

The above described procedure may also be used with waxes dissolved inan organic solvent. All the waxes in Table 1 may be dissolved in organicsolvents such as petroleum ether, chloroform or acetone. However thewater soluble wax is less soluble in these organics and consequently Iprefer to use any of the others in the table. Any of these solvents canbe readily driven ofi by the fourth step in the process which becomes asolvent evaporating step using either a belt conveyor adjacent to asource of heat or an oven.

Still another modification of the process can be used. I may melt thewax and add it to the abrasive in molten condition. Practically any waxcan be melted including all those listed in the table. When carrying outthe process in this manner it is desirable and in many cases necessaryas a practical matter to heat the abrasive grain. It is preferable toheat the abrasive grain to about the melting point of the wax. Thus,proceeding in this manner, I may first heat the abrasive grain to thedesired temperature and at the same time melt the wax. Then the mixingmachine is charged with the abrasive grain and preferably the mixing panand the grain are kept hot as by theuse of a heating lamp.

Now, while the machine is in operation, the liquid wax is added. Whenthe wax has coated all the granules, the bond is added while continuingthe mixing. It is desirable that the bond also be heated before it isadded to the pan.

Table Wax Origin H Chemistry Melting Point Vegetable... Fatty AcidGlyceride 183 F. do 0 130 F.

Around 170 F. 175 F. don..." do various.

Chlorinated Diphenyl 194 F. d Chlorinated Hydrocarbon 183 F.

Amide Fatty Acid and Ethylene 275 F Diaminc.

Water Soluble Pol Ethylene Glycol (Molecular 130 F.

wax. eighti Beeswax Animal Fatty Acid Glyceride.....' 130 F.Candellila... Vegetable... .do 130 F.

The particular wax product which is now pre- 15 Then the mixture is,dumped and cooled, and

when it is near room temperature it is screened, then recharged into aclean mixing pan and the anti-sticking agent is added while the mixer isin operation.

One important feature of the dry granular mix according to the inventionis that it is free flowing. Using the wax first described, the mix hasan angle or repose of about 30. The automatic molding machines which areused to press the dry granular mix into green articles operate muchbetter if the mixture used is free flowing. Such machines have a hopperwhich is charged with the material and ducts to lead the material to amold cavity'with means to stop and start the flow of material, andplungers to press the material. Accurate pressed pieces of the samevolume structure can be made if the material is free flowing. If thematerial does not flow freely the machine will fail to fill the moldcavity or will jam or clog. In other words, if the material is not freeflowing the purpose of the automatic machine may be defeated so far asproduction is concerned and also the machine may fail to produce uniformstrong pieces. If the dry granular mix is made in accordance with thevarious embodiments of this invention it is sufficiently free flowing toenable automatic molding machines to operate continuously, producingpressed green abrasive articles and the like which are uniformlyaccurately dimensioned and have the same weight and the same volumestructure. It is possible, using the dry granular mix of the invention,molding it in an automatic molding machine and then firing the greenarticles, to produce grinding wheels which in diameter thickness andsize of the central hole vary from each other by no more than two orthree thousandths of an inch. Thus no truing operation on the grindingwheels is required and they are made to closer tolerances than washeretofore considered commercially practicable.

Another feature of the present invention is that molded pieces made fromthe dry granular mix hereof may be immediately fired without anyintervening drying or baking operation after molding. This saves a greatdeal of handling of the pressed pieces, it saves time and labor, and itavoids the accumulation of inventory.

However, if the varying demands of commerce and industry make itdesirable to store pressed green unfired grinding wheels, those madewith the dry granular mix of the invention can be stored for a longertime than was hitherto practicable since they are stronger and willretain their strength over a long period. Perhaps a more importantfeature however is that the dry granular mix of the invention as suchand before pressing into bodies can be stored for an indefinite periodwithout deterioration. There is every reason to suppose that the drygranular mix of the invention can be stored for years and stillsuccessfully used.

The abrasives used in carrying out this invention are particularly thewidely used abrasives fused alumina and silicon carbide (of variousgrades). Other forms of alumina such as corundum may be used. These havea hardness of 9 or more on Mohs scale. Emery, which is a natural butsomewhat impure alumina, may be used if desired but is not likely to beused because it has been largely superceded for grinding wheels by theelectric furnace products referred to as fused alumina. Emery has ahardness around 9 on Mohs scale.

All of the above are refractory as well as hard, that is they do notmelt at the vitrifying temperatures. Diamonds are refractory in knownfiring procedures with the vitrifiable bonds suitable for diamonds nowknown to the art. The abrasive.

is therefore properly described as hard refractory material and it ismore refractory than the vitrifiable bond.

This invention involves a new method of making abrasive products such asgrinding wheels. After a dry granular mix as described herein has beenmade, it is placed in the hopper of an automatic molding machine whichturns out pressed green wheels as above described. These are then takento a suitable kiln, preferably for high speed production to atunnelkiln, and vitrified at a maturing temperature for example of cone12. This involves a top temperature usually of about 1200" C. orslightly above. During firing the wax and the anti-sticking agent burnand actually give off heat assisting the vitrification. It is found thatthe wax and the anti-sticking agent practically completely disappearleaving only a trace of ash which is not deleterious. In accordance withthis invention, therefore, the

. manufacture of abrasive products has been greatly accelerated becauseautomatic molding machines are used for the molding of the wheels. It ismy belief that no one prior to my inventions hereof and of my aforesaidapplication Serial No. 681,769 successfully made grinding wheels inautomatic molding machines and by successfully I mean without cloggingof the molding machines and with the production of perfect pieces inquantities. Yet automatic molding ma:

chines for the manufacture of pressed products out of powders, such asfor example tablets, have been available for more than 50 years.

It will be seen that in every case the antisticking agent is a fine mealcontaining at least 10% and not more than 50% of fatty ester, where theword meal is used in the well-known sense of a product made by grindingor otherwise comminuting seeds or nuts. Furthermore the variousanti-sticking agents herein described can be properly defined as cocoapowder, rape seed powder, linseed powder, etc. The fatty ester in everyone of the seeds mentioned is a glycerine ester of a fatty acid.

It will thus be seen that there has been provided according to thisinvention a dry granular mix, a method of making it and a method ofmaking grinding wheels according to which the various objects in=inabove set forth together with many thoroug .i'y practical advantagesare successfully achieved. As many possible embodiments may be made ofthe above invention and as many changes might be in the embodiment aboveset forth, it is to be understood that all matter hereinbefore set forthis to be interpreted as illustrative and not in a limiting sense.

Iii

I claim:

1. A dry granular mix comprising particles of hard refractory materialeach coated with a considerable number of fine particles of vitrifiableceramic bond mixed with wax, the bond and wax forming an envelope whichsurrounds a particle, each particle of refractory material having suchenvelope, and a coating of a fine meal derived from vegetable seed, saidfine meal containing at least 10% and not more than 50% of fatty ester,on each such envelope.

2. A dry granular mix comprising particles of hard refractory materialeach coated with a considerable number of fine particles of vitrifiableceramic bond mixed with wax having a melting point at least as high asF., the bond and wax forming an envelope which surrounds a particle,each particle of refractory material having such envelope and a coatingof a fine meal derived from vegetable seed, said fine meal containing atleast 10% and not more than 50% of fatty ester, on each such envelope.

3. A pressed green unfired ceramic body which is integral for handlingand which comprises a great number of particles of refractory abrasivegrain, each particle coated with an envelope of powdered vitrifiableceramic bond mixed with wax and each envelope having a ruptured coatingof a fine meal derived from vegetable seed, said fine meal containing atleast 10% and not more than 50% of fatty ester, thereon, and theenvelopes being stuck together adhesively by said wax to make said bodyintegral.

4. A pressed green unfired ceramic body which is integral for handlingand which comprises a great number of particles of refractory abrasivegrain, each particle coated with an en velope of powdered vitrifiableceramic bond mixed with wax having a melting point at least as high as130 F. and each envelope having a ruptured coating of a fine mealderived from vegetable seed, said fine meal containing at least 10% andnot more than 50% of fatty ester, thereon, and the envelopes being stucktogether adhesively by said wax to make said body interal.

5. The method of making a dry granular mix for the subsequentmanufacture of vitrified products which comprises mixing a quantity ofrefractory abrasive grain with a water emulsion of wax until eachparticle of the grain is coated with said wax emulsion, then adding aquantity of dry powdered vitrifiable ceramic bond of particle sizesmaller than that of the grain, further mixing the vitrifiable bond withthe wax emulsion coated grain until the latter has picked upsubstantially all of the former thus forming an envelope of vitrifiablebond and wax on each particle, then drying the mix to evaporate thewater, then screening the mix, then adding a fine meal derived fromvegetable seed, said fine meal containing at least 10% and not more than50% of fatty ester and further mixing to coat each such envelope withsaid fine meal containing at least 10% and not more than 50% of fattyester.

6. The method of making a dry granular mix for the subsequentmanufacture of vitrified products which comprises mixing a quantity ofrefractory abrasive grain with a water emulsion of wax having a meltingpoint at least as high as 130 F. until each particle of the grain iscoated with said wax emulsion, then adding a quantity of dry powderedvitrifiable ceramic bond of particle size smaller than that of thegrain, further particle, then drying the mix to evaporate the water.then screening the mix, then adding a fine meal derived from vegetableseed, said fine meal containing at least and not more than 50% of fattyester and further mixing to coat each such envelope with said fine mealcontain- 1 ing at least 10% and not more than 50% of fatty ester.

7. The method of making a dry granular mix for the subsequentmanufacture of vitrified products which comprises mixing a quantity ofrefractory abrasive grain with melted wax until each particle of thegrain is coated with wax, then adding a quantity of dry powderedvitrifiable ceramic bond of particle size smaller than that of thegrain, further mixing the vitrifiable'bond with the wax coated grainuntil the latter has picked up substantially all of the former thusforming an envelope of vitrifiable bond and wax on each particle, lateradding a fine meal derived from vegetable seed, said fine mealcontaining at least 10% and not more than 50% fatty ester and furthermixing to coat each such envelope with said fine meal containing atleast 10% and not more than 50% fatty ester.

8. The method of making a dry granular mix for the subsequentmanufacture of vitrified products which comprises mixing a quantity ofrefractory abrasive grain with a solution of wax until each particle ofthe grain is coated with such solution, then adding a quantity of drypowdered vitrifiable ceramic bond of particle size smaller than that ofthe grain, further mixing the vitrifiable bond with the grain coatedwith solution of wax until the latter has picked up substantially all ofthe bond thus forming an envelope of bond wax and liquid solvent on eachparticle, then heating the mix to evaporate the solvent, then screeningthe mix, then adding a fine meal derived from vegetable seed, said finemeal containing at least 10% and not more than i of fatty ester andfurther mixing to coat each such envelope with said fine meal containingat least 10% and not more than 50% of fatty ester.

9. The method of making a dry granular mix 50 for the subsequentmanufacture of vitrified products which comprises coating each particleof a quantity of refractory abrasive grain with dry powdered vitrifiablebond and wax to form an envelope thereof on each such particle, then tomixing said particles of grain having such envelopes with a fine mealderived from vegetable seed, said fine meal containing at least 10% andnot more than 50% of fatty ester to coat each such envelope with saidfine meal containing at 0 least 10% and not more than 50% of fattyester.

10. The method of making grinding wheels and the like which comprisescoating a quantity of refractory abrasive grain with wax in a fiowablecondition, adding dry powdered vitrifiable ceramic bond and mixing untilthe bond has been picked up by the wax coated grain thus forming anenvelope of vitrifiable bond and wax on each particle of the abrasivegrain, then hardening the wax, screening the mixture, then add- 7" turein the hopper of an automatic molding machine, setting the machine inoperation thus producing pressed "green" wheels, then vitrifying thegreen wheels in a kiln.

11. Method of making grinding wheels and the like according to claim 10in which the wax in a fiowable condition is a water emulsion of wax andin which, prior to screening the mixture, most of the water is drivenfrom the said emulsion of wax by heating thus hardening the wax.

12. A dry granular mix comprising particles of hard refractory materialeach coated with a -melting point of at least as high as 130 F., the

bond and wax forming an envelope which surrounds a particle, eachparticle of refractory material having such envelope, and a coating ofcocoa powder containing at least 10% and not more than 50% of cocoabutter on each such envelope.

14. A pressed green" uniired ceramic body which is integral for handlingand which comprises a great number of particles of refractory abrasivegrain, each particle coated with an envelope of powdered vitrifiableceramic bond mixed with wax and each envelope having a ruptured coatingof cocoa powder containing at least 10% and not more than 50 (7p ofcocoa butter thereon, and the envelopes being stuck together adhesivelyby said wax to make said body integral.

15. A pressed green" unfired ceramic body which is integral for handlingand which comprises a great number of particles of refractory abrasivegrain, each particle coated with an envelope of powdered vitrifiableceramic bond mixed with wax having a melting point at least as high as130 F. and each envelope having a ruptured coating of cocoa powdercontaining at least 10% and not more than 50% of cocoa butter thereon,and the envelopes being stuck together adhesively by said wax to makesaid body integral.

16. The method of making a dry granular mix for the subsequentmanufacture of vitrified products which comprises mixing a quantity ofrefractory abrasive grain with a water emulsion of wax until eachparticle of the grain is coated with said wax emulsion, then adding aquantity of dry powdered vitrifiable ceramic bond of particle sizesmaller than that of the grain, further mixing the vitrifiable bond withthe wax emui sion coated grain until the latter has picked upsubstantially all of the former thus forming an envelope of vitrifiablebond and wax on each particle, then drying the mix to evaporate thewater, then screening the mix, then adding cocoa powder containing atleast 10% and not more than 50% of cocoa butter and further mixing tocoat each such envelope with said cocoa powder containing at least 10%and not more than 50% of cocoa butter.

17. The method of making a dry granular mix for the subsequentmanufacture of vitrified each envelope, placing a quantity of themixproducts which comprises mixing a quantity of refractory abrasivegrain with a water emulsion of wax having a melting point at least ashigh as 130 F. until each particle of the grain is coated with said waxemulsion, then adding a quantity of dry powdered vitrifiable ceramicbond of particle size smaller than that of the grain, further mixing thevitrifiable bond with the wax emulsion coated grain until the latter haspicked up substantially all of the former thus forming an envelope ofvitriflable bond and wax on each particle, then drying the mix toevaporate the water, then screening the mix, then adding cocoa powdercontaining at least 10% and not more than 50% of cocoa butter andfurther mixing to coat each such envelope with said cocoa powdercontaining at least 10% and not more than 50% of cocoa butter.

18. The method of making a dry granular mix for the subsequentmanufacture of vitrified products which comprises mixing a quantity ofrefractory abrasive grain with melted wax until each particle of thegrain is coated with wax,

'then addin a quantity of dry powdered vitrified 19. The method ofmaking a dry granular mix for the subsequent manufacture of vitrifiedproducts which comprises mixing a quantity of refractory abrasive grainwith a solution of wax until each particle of the grain is coated withsuch solution, then adding a quantity of dry powdered vitrifiableceramic bond of particle size smaller than that of the grain, furthermixing the vitrifiable bond with the grain coated with solution of waxuntil the latter has picked up substantially all of the bond thusforming an envelope of bond wax and liquid solvent on each particle,then heating the mix to evaporate the solvent, then screening the mix,then adding cocoa powder containing at least 10% and not more than 50%of cocoa butter and further mixing to coat each such envelope with saidcocoa powder containing at least 10% and not more than 50% of cocoabutter.

20. The method of mamng a dry granular mix for the subsequentmanufacture of vitrified products which comprises coating each particleof a quantity of refractory abrasive grain with dry powdered vitriflablebond and wax to form an envelope thereof on each such particle, thenmixing said particles of grain having such envelopes with cocoa powdercontaining at least 10% and not more than of cocoa butter to coat eachsuch envelope with said cocoa powder containing at least 10% and notmore than 50% of cocoa butter. 4

21. The method of making grinding wheels and the like'which comprisescoating a quantity of refractory abrasive grain with wax in a flowablecondition, adding dry powdered vitrifi; able ceramic bond and mixinguntil the bond has been picked up by the wax coated grain thus formingan envelope of vitrifiable bond and wax on each particle of the abrasivegrain, then hardening the wax, screening the mixture, then adding cocoapowder containing at least 10% and not more than 50% ofcocoa butter tothe mixture and mixing to form a coating of said cocoa powder containingat least 10% and not more than 50% of cocoa butter on each envelope,placing a quantity of the mixture in the hopper of an automatic moldingmachine, setting the machine in operation thus producing pressed "greenwheels, then vitrifying the green wheels in a kiln.

22. Method of making grinding wheels and the like according to claim 21in which the wax in a flowable condition is a water emulsion of wax andin which, prior to screening the mixture, most of the water is drivenfrom the said emulsion of wax by heating thus hardening the wax.

WALLACE L. HOWE.

REFERENCES CITED 'Ihe following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Condensed Chem. Dict., 3rdedition, Reinhold Pub. Corp., 1942, page 672.

1. A DRY GRANULA MIX COMPRISING PARTICLES OF HARD REFRACTORY MATERIALEACH COATED WITH A CONSIDERABLE NUMBER OF THE FINE PARTICLES OFVITRIFLABLE CERAMIC BOND MIXED WITH WAX, THE BOND AND WAX FORMING ANENVELOPE WHICH SURROUNDS A PARTICLE EACH PARTICLE OF REFRACTORY MATERIALHAVING SUCH ENVELOPE, AND A COATING OF THE FINE MEAL DERIVED FROMVEGETABLE SEED, SAID FINE MEAL CONTAINING AT LEAST 10% AND NOT MORE THAN50% OF FATTY ESTER, ON EACH SUCH ENVELOPE.